Sheet material and its production method

ABSTRACT

PROBLEM 
     To effectively utilize plant residue such as soybean hulls, rapeseed meal, rice bran, rice husk, and cacao husk. 
     SOLUTION 
     When forming sheet material from a mixture of burned plant material and fibrous material by a wet-process sheet production method, the burned plant material is one of a burned material of rice husk, a burned material of rice bran, a burned material of soybean hulls, a burned material of inner skin of peanut, a burned material of conduit side wall portion of seed plant or a burned material of cacao husk, and the fibrous material is one of a organic fiber derived from thermoplastic resin including polyolefin consisting of polyethylene and polypropylene, polyester, polyamide, vinyl chloride, polyacrylonitrile, polyvinyl chloride and aramid, a fiber derived from thermosetting resin including kynol, a natural fiber including cotton, wool, etc., a semisynthetic fiber, an inorganic fiber including glass fiber and carbon fiber, a metal fiber including iron, copper, stainless steel and steel, a metalized fiber with electroless plating applied on short fibers including synthetic resin and inorganic material, furthermore, a combination of these short fibers.

FIELD OF THE INVENTION

The present inventions is related to a sheet material and its productionmethod, particularly, a sheet material and its production method using aburned plant material such as burned material of rice husk, burnedmaterial of rice bran, burned material of soybean hulls, and burnedmaterial of cacao husk.

BACKGROUND OF THE INVENTION

Patent Document 1 discloses the idea to use industrially a burned plantmaterial obtained by burning a plant including grain residue such assoybean hulls, rapeseed meal, rice bran, and rice husk.

Patent Document 1: JPA2010-161337

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

By the way, in recent years, reuse is discussed from a viewpoint ofecology for grain residue such as soybean hulls, rapeseed meal, ricebran, and rice husk. In particular, as disclosed in Patent Document 1,interesting data have been obtained in a burned material of grainresidue mainly from a viewpoint of electrical characteristics.

The present invention makes it a problem to use effectively grainresidue such as soybean husk, rapeseed meal, rice bran, and rice hulls.

Means of Solving the Problems

The present inventors burned grain residue such as soybean hulls,rapeseed meal, rice bran, rice husk, and cacao husk, and produced asheet material using the burned plant material and fibrous material,then, measured electrical characteristics, etc. As a result, it wasfound that the sheet material has excellent electromagnetic shieldingcharacteristic and electromagnetic wave absorption characteristic.

The sheet material of the present invention to solve the above problemis formed by a wet-process sheet production method from a mixture ofburned plant material and fibrous material. In addition, the productionmethod of a sheet material of the present invention is to form a sheetby wet-process sheet production using the sheet making slurry obtainedby mixing fibrous material and burned plant material in water.

As burned plant material, burned materials of soybean hulls, rapeseedmeal, rice bran, rice husk, soybean chaff, inner skin of peanut, conduitside wall portion of seed plant, cacao husk, etc. are included. And itwas found that electromagnetic shielding characteristic, etc. arechanged by changing mixing ratio between those burned materials andfibrous material, or by changing paper weight in gsm of sheet material,or by mixing of metal filler, matrix, etc. Said mixing ratio, etc. canbe determined according to the frequency band of electromagnetic wave tobe shielded, etc. In addition, the mixing ratio between burned plantmaterial and fibrous material to optimize electromagnetic shieldingcharacteristic, etc. was also found.

As a result of the study of the present inventors, it was found that thetype of burned plant material to be a material of sheet material can beselected according to the application of sheet material. For example, inorder to produce a sheet material having an excellent electromagneticshielding characteristic, for example, a burned material of soybeanhulls or a burned material of cacao husk can be selected as a material.In addition, in order to produce a sheet material having an excellentelectromagnetic wave absorption characteristic, for example, a burnedmaterial of cacao husk, a burned material of rice husk or a burnedmaterial of rice bran can be selected as a material. Therefore, in orderto produce a sheet material having an excellent electromagneticshielding characteristic and an excellent electromagnetic waveabsorption characteristic, a burned material of cacao husk includingspiral portion, etc. can be selected as a material.

In addition, regarding the fibrous materials of sheet material of thepresent invention, since it is acceptable if they can even immobilize aburned plant material, these types are particularly unquestioned. As anexample, they are shown below, (1) organic fiber derived fromthermoplastic resin including polyolefin consisting of polyethylene andpolypropylene, polyester, polyamide, vinyl chloride, polyacrylonitrile,polyvinyl chloride, aramid, etc., (2) fiber derived from thermosettingresin including kynol, etc., (3) natural fiber including cotton, wool,cellulose pulp, etc., (4) semisynthetic fiber, (5) inorganic fiberincluding glass fiber, carbon fiber, etc., (6) metal fiber includingiron, copper, stainless, steel, etc., (7) furthermore, combination ofthese short fibers. These fibrous materials can also serve as areinforcement material of sheet material.

In order to mold the sheet material, the matrices consisting of powderyor fibrous thermosetting resin or thermoplastic resin are added at thesame time when performing sheeting, or, the matrices consisting ofthermosetting resin or thermoplastic resin of liquid state may beimpregnated into a sheet material

In order to produce a sheet material having electromagnetic shieldingeffect in a wide frequency band, as described below, since a burnedplant material can cover a relatively low frequency band, it is betterto use fibrous or powdery metal filler having excellent electromagneticshielding effect in a high frequency band. Also, a metal filler may befibrous or powdery organic filler or inorganic filler which is appliedmetal plating.

EMBODIMENT OF THE INVENTION

Referring to drawings, embodiments according to the present inventionare described hereinafter.

Embodiment 1

In this embodiment, although a case that a burned material of cacao huskis used as a material of sheet material is mainly explained as aexample, a case that a burned material of soybean hulls, a burnedmaterial of rapeseed meal, a burned material of rice bran, a burnedmaterial of rice husk, a burned material of soybean chaff, a burnedmaterial of inner skin of peanut or a burned material of conduit sidewall portion of seed plant is used as a material of sheet material isalso same. In addition, a production method of burned material ofsoybean hulls, etc. is the same as a production method of burnedmaterial of cacao husk.

In addition, the cacao husk in this embodiment is mainly the skin itselfwhich covers plural cocoa beans contained in cacao, and it may be calledcacao shell. In this embodiment, although various experiments andevaluations are performed with the contents described above, the cacaohusk in this embodiment includes not only the cacao husk but also themixture of the cacao husk and the skin covering cocoa beans.

In this embodiment, for example, at a temperature of approx. 600 [° C.]to 3000 [° C.], using a carbonization apparatus such as a holdingfurnace or a rotary kiln, the burned material of cacao husk is obtainedby burning cacao husk for about 3 hours at the attained temperature inan inert gas atmosphere with nitrogen gas, etc. or in a vacuumcondition, selectively. Then, the burned material of cacao husk ispulverized selectively and then sieved using a mesh, for example, of a106 μm wire mesh.

As a result, about 80% of the entire burned material of cacao huskbecomes 85 μm or below. In this case, the median diameter is, forexample, approx. 25 μm. Hereinafter, in the case that the burningtemperature is clearly specified as 900 [° C.], the median diameter whenthe burned material of cacao husk is pulverized is approx. 25 μm.

The median diameter is measured by a laser diffraction particle sizeanalyzer, for example, SALD-7000 manufactured by SHIMADZU Corporation.In this embodiment, a burned material of cacao husk whose mediandiameter is approx. 10 μm to approx. 60 μm may be used, and a burnedmaterial whose minimum median diameter is approx. 1 μm by those furtherselective pulverizing may also be used.

In addition, pulverizing herein refers to a pulverization of apre-pulverizing material to reduce its median diameter by about onedecimal order. Therefore, it refers that a median diameter of 30 μmbefore pulverization is pulverized to 3 μm. However, pulverizing doesnot refer to exactly reducing the median diameter before pulverizationby approx. one decimal order, and it also includes pulverizing to reducethe median diameter before pulverization to ⅕- 1/20. In this embodiment,the pulverization is carried out so that the median diameter afterpulverization becomes 1 μm at the smallest.

FIG. 1 shows a schematic production process diagram of the sheetmaterial using burned material of cacao husk. First, after repeatedcrushing against cacao husk until the size of crushed material becomesabout 1.0 mm to 3.0 mm by a known crusher, it is set in a carbonizationapparatus. At this time, selectively, when it is impregnated withphenolic resin such as resol-type phenolic resin, the strength andcarbon content of burned material of cacao husk can be improved.However, please note that said impregnation itself is not essential forproducing the sheet material of this embodiment.

Second, the cacao husk is heated at the rate of approx. 2 [° C.] perminute in a nitrogen gas atmosphere to reach a prescribed temperaturesuch as 700 [° C.]-1500 [° C.] (for example, 900 [° C.]). Then thecarbonizing burning treatment is performed for several hours to severalweeks, for example, at the attained temperature.

Next, the fibrous material such as, aramid fiber and polyethylene fiberis introduced in a mixer having high shear property such as a juicermixer, a pulper mixer, and a henschel mixer with plenty of water, and isdispersed and mixed. In addition, the fibrillation treatment of fibrousmaterial may be possible using a defibration device such as a beater anda refiner in order to improve the tangle of fibrous material and theparticle collection property of fibrous material in the case of sheetmaterial.

Then, water dispersed fibrous material is introduced in an agitatedvessel with propeller impeller, furthermore, a burned cacao husk withpulverization or without pulverization is introduced. The pulverizationcondition is as described above. In addition, the mixing ratio betweenburned cacao husk and aramid fiber, etc. will be described below withvarious measurement results. At this time, if necessary, variousadditives such as metal filler may be introduced in the agitated vessel.

And then, rotating the propeller impeller, the burned cacao husk and thevarious additives are dispersed and mixed in water in which a fibrousmaterial is dispersed. At this time, the rotational speed of thepropeller impeller may be about 50 [rpm] to 500 [rpm] so as to maintainthe carbonaceous shape of burned cacao husk.

Then, adding a particle collection agent in the agitated vessel, thesheet making slurry of 0.01% to 1.0% concentration is obtained byagitation and mixing at low speed. The particle collection agent may beused in typical paper-making process of sheet making, or, in watertreatment, it is also referred as a flocculant.

Next, the sheet making slurry is subjected to wet-process sheetproduction. More specially, for example, the total amount of sheetmaking slurry obtained is introduced in a box-type paper machine ofabout 300 [mm]×300 [mm] covered with 100 mesh square sheet making wiremesh, then, a wet state sheet is obtained by performing the dischargefiltration of water and the suctioning, squeezing and dewatering fromthe bottom of the paper machine. And then, it is dried in a hot aircirculation dryer at about 100° C.

It is cut into an appropriate size and filled in a metal mold which isheated to about 130° C., and then, it is pressed under the conditions ofabout 20 [kgf/cm²] as molding pressure and about 5 minutes as moldingtime in a compression molding machine, after that, when it is cooled toabout 100° C. under pressurized condition, the sheet material of thepresent embodiment can be obtained. The heating temperature may be equalto or higher than the curing temperature of thermosetting resin or themelting temperature of thermoplastic resin to be a matrix. And themolding pressure may also be selected appropriately depending on thetarget thickness of sheet material. In addition, as a production processof sheet material, it is not mandatory to include the compressionmolding using a metal mold, for example, it can also be formed by a rollpress.

FIG. 2 shows charts indicating the measurement results of theelectromagnetic shielding characteristics of the sheet material producedthrough a pulverization process of burned material of cacao husk. Thelateral axis and vertical axis of FIG. 2 indicate frequency [MHz] andelectromagnetic shielding effectiveness (SE) [dB] respectively. Inaddition, these electromagnetic shielding characteristics were obtainedby using Shield Material Evaluator (TR17301A manufactured by AdvantestCorporation) and Spectrum Analyzer (TR4172 manufactured by AdvantestCorporation) at Yamagata Research Institute of Technology, OkitamaBranch.

FIG. 2( a) shows the electromagnetic shielding characteristic in thecase that the paper weight in gsm of burned material of cacao husk is2000 [g/m²]. FIG. 2( b) shows the electromagnetic shieldingcharacteristic in the case that the paper weight in gsm of burnedmaterial of cacao husk is 3000 [g/m²]. Incidentally, when the plane sizeof sheet material is about 300 [mm]×300 [mm], the thickness is about 3.0[mm] in the case that the paper weight in gsm of sheet material is 2000[g/m²], the thickness is about 4.5 [mm] in the case that the paperweight in gsm of sheet material is 3000 [g/m²].

First, upon measuring the electromagnetic shielding characteristics ofsheet material, the sheet material that the mixing ratios of burnedmaterial of cacao husk against the entire sheet material are 50 [wt. %],60 [wt. %], 70 [wt. %] and 80 [wt. %] is produced respectively.

In FIG. 2( a), if the mixing ratio of burned material of cacao husk isincreased more, it can be seen that the electromagnetic shieldingeffectiveness of sheet material is increased more. Here, as theelectromagnetic shielding effectiveness, generally, 20 [dB] or abovewhich can shield electromagnetic wave 99% or above is one indicator fora practical rough standard. The sheet material of the present embodimentis 20 [dB] or above in the frequency range 100 [MHz] or below in generalin the case that the mixing ratio of burned material of cacao huskagainst the entire sheet material is 80 [wt. %]. Therefore, it isunderstood that the sheet material of the present embodiment isexcellent electromagnetic shielding characteristic.

In addition, when compared with FIG. 2( a) and FIG. 2( b), if the paperweight in gsm will be 3000 [g/m²], the electromagnetic shieldingeffectiveness is increased in each of case where the mixing ratios ofburned material of cacao husk against the entire sheet material are 50[wt. %], 60 [wt. %] and 70 [wt. %]. Therefore, if the mixing ratio ofburned material of cacao husk against the entire sheet material becomes80 [wt. %], it is unlikely that there is a dramatic change in theelectromagnetic shielding characteristic even if the paper weight in gsmis 2000 [g/m²], 3000 [g/m²] or is increased more.

In the case that the paper weight in gsm is 3000 [g/m²], if the mixingratio of burned material of cacao husk against the entire sheet materialis 60 [wt. %] or above, the electromagnetic shielding characteristic ofsheet material is not much difference. Therefore, in this case, it isunlikely that there is a dramatic change in the electromagneticshielding characteristic even if the mixing ratio of burned material ofcacao husk against the entire sheet material is increased more.

That is, when the total amount of burned material of cacao husk in thesheet material has reached a certain amount, subsequently, it isunlikely that the electromagnetic shielding characteristic is improvedeven if the total amount of burned material of cacao husk is increasedmore. Therefore, in the case that the sheet material is produced usingburned material of cacao husk, it is possible that the burned materialof cacao husk can be reasonable amount and no-wasted amount.

FIG. 3 shows charts indicating the measurement results of theelectromagnetic shielding characteristics of the sheet material producedwithout going through a pulverization process of burned material ofcacao husk, it is corresponding to FIG. 2. In addition, all measurementmethods of electromagnetic shielding characteristic describedhereinafter are the same as described above.

As it is obvious from FIG. 3, surprisingly, the electromagneticshielding effectiveness is significantly increased overall in case ofwithout going through a pulverization process. That is, even if thepaper weight in gsm is 2000 [g/m²] or 3000 [g/m²], in the case of 600[MHz] or below which is the frequency band of the upper measurementlimit shown in FIG. 3, even if the mixing ratio of burned material ofcacao husk against the entire sheet material is any of 50 [wt. %], 60[wt. %], 70 [wt. %] or 80 [wt. %], the electromagnetic shieldingeffectiveness is approximately more than 20 [dB], even from seeing atthe frequency band and even from seeing at the mixing ratio, theelectromagnetic shielding effectiveness is significantly increasedoverall.

From this, the sheet material produced without going through apulverization process against burned material of cacao husk is possibleto obtain relatively excellent electromagnetic shielding characteristic,even if the mixing ratio of burned material of cacao husk against theentire sheet material is kept low relatively or even if the paper weightin gsm of sheet material is reduced relatively. In other words, thesheet material produced without going through a pulverization processagainst burned material of cacao husk is possible to produce a sheetmaterial inexpensively because it only needs to use a small amount ofburned material of cacao husk.

According to FIG. 3( b), in the mixing ratio as a measurement target, inthe case that the mixing ratio of burned material of cacao husk againstthe entire sheet material is 70 [wt. %], the electromagnetic shieldingcharacteristic is best. That is, with regard to the electromagneticshielding characteristic, it can be said that the mixing ratio of burnedmaterial of cacao husk against the entire sheet material is generally 70[wt. %].

FIG. 4 shows charts indicating the measurement results of theelectromagnetic shielding characteristics of the sheet material producedthrough a pulverization process of burned material of soybean hulls, itis corresponding to FIG. 2.

FIG. 5 shows charts indicating the measurement results of theelectromagnetic shielding characteristics of the sheet material producedwithout going through a pulverization process of burned material ofsoybean hulls, it is corresponding to FIG. 3.

In contrast to FIG. 4, FIG. 5 and FIG. 2, FIG. 3 respectively, althoughthe electromagnetic shielding effectiveness is different, some commonpoints can be found. More specially, they are common in these pointsthat, in the case of without going through a pulverization process, theelectromagnetic shielding level of sheet material is high, the mixingratio of burned plant material against the entire sheet material islikely to be good at generally 70 [wt. %], the paper weight in gsm ofsheet material is good to be the greater, in the view point ofelectromagnetic shielding characteristic.

In addition, in the sheet material produced using rice husk withoutpulverization, the electromagnetic shielding effectiveness 20 [dB] orabove is confirmed at the frequency band 100 [MHz] or below. On theother hand, in the case of sheet material produced using rice bran, evenif the best condition, it is able to produce only the sheet material inwhich the electromagnetic shielding effectiveness is slightly more than20 [dB].

For the above reasons, in order to produce a sheet material particularlyexcellent in electromagnetic shielding characteristic, it can be seenthat the burned material of cacao husk and the burned material ofsoybean hulls are better to be used as material. However, regarding theelectromagnetic shielding member which is generally commerciallyavailable, most of electromagnetic shielding effectiveness falls in therange of 5 [dB] to 25 [dB]. According to this, the electromagneticshielding effectiveness of 20 [dB] used as an index in the presentembodiment is of a higher level. Even in any of the burned material ofrice husk, rice bran, cacao husk or soybean hulls, the electromagneticshielding effectiveness 5 [dB] or above is confirmed at the frequencyband 600 [MHz] or below. Therefore, the sheet material of the presentembodiment is able to achieve the same level as those of theelectromagnetic shielding member in commercial level, even though usingany burned plant material which is the measurement object here.

FIG. 6 shows charts indicating the measurement results of theelectromagnetic wave absorption characteristic of the sheet materialproduced through a pulverization process of burned material of cacaohusk. FIG. 6( a) shows the measurement results of the electromagneticwave absorption characteristic in the case that the paper weight in gsmof burned material of cacao husk is 2000 [g/m²], FIG. 6( b) shows themeasurement results of the electromagnetic wave absorptioncharacteristic in the case that the paper weight in gsm is 3000 [g/m²].

For measuring the electromagnetic wave absorption characteristics shownin FIG. 6, the sheet material with a size of 300 [mm]×300 [mm] ismounted on a metallic plate with the same size, and the sheet materialis irradiated with the incident waves of frequencies plotted in FIG. 6so as to measure the energy of the reflected waves from the sheetmaterial, thus the energy difference between the incident wave and thereflected wave, that is, the electromagnetic wave absorption (energyloss) is calculated. The measurement is performed based on the arch testmethod by using an arch type electromagnetic wave absorption measuringapparatus.

AS shown in FIG. 6( a), in the case that the paper weight in gsm ofburned material of cacao husk is 2000 [g/m²], at the time that themixing ratio of burned material of cacao husk against the entire sheetmaterial is 60 [wt. %], the electromagnetic wave absorption with a peakaround 6000 [MHz] can be confirmed. For the electromagnetic waveabsorption, in general, one indicator is whether it exceeds the level of−20 [dB]. Then, since the peak is about −35 [dB], it is found that theabsorption amount is significantly higher than the indicator.

As shown in FIG. 6( b), in the case that the paper weight in gsm ofburned material of cacao husk is 3000 [g/m²], at the time of the mixingratio of burned material of cacao husk against the entire sheet materialis 50 [wt. %], the electromagnetic wave absorption with a peak around5000 [MHz] can be confirmed. Since the electromagnetic wave absorptionis about −42 [dB], it is found that the absorption amount issignificantly higher than the indicator.

According to FIG. 6( a) and FIG. 6( b), by appropriate selection of thepaper weight in gsm and the mixing ratio of burned material of cacaohusk against the entire sheet material, the electromagnetic waveabsorbing sheet material targeted a desired frequency band can beproduced.

FIG. 7 shows charts indicating the measurement results of theelectromagnetic wave absorption characteristic of the sheet materialproduced through a pulverization process of the burned material of ricehusk. FIG. 7( a) shows the measuring results of the electromagnetic waveabsorption characteristic in the case that the paper weight in gsm ofburned material of rice husk is 2000 [g/m²], FIG. 7( b) shows themeasuring results of the electromagnetic wave absorption characteristicin the case that the paper weight in gsm is 3000 [g/m²]. Thismeasurement is performed based on the arch test method.

As shown in FIG. 7( a), in the case that the paper weight in gsm ofburned material of rice husk is 2000 [g/m²], when the mixing ratio ofburned material of rice husk against the entire sheet material is 70[wt. %], the electromagnetic wave absorption with a peak around 6000[MHz] can be confirmed. Since the electromagnetic wave absorption isabout −35 [dB], it is found that the absorption amount is significantlyhigher than the indicator. In addition, when the mixing ratio of burnedmaterial of rice husk against the entire sheet material is 60 [wt. %],the electromagnetic wave absorption with a peak around 6500 [MHz] can beconfirmed. Since the electromagnetic wave absorption is about −27 [dB],it is found that the absorption amount significantly higher than theindicator.

As shown in FIG. 7( b), in the case that the paper weight in gsm ofburned material of rice husk is 3000 [g/m²], when the mixing ratio ofburned material of rice husk against the entire sheet material is 60[wt. %], the electromagnetic wave absorption with a peak around 4500[MHz] can be confirmed. Since the electromagnetic wave absorption isabout −28 [dB], it is found that the absorption amount is significantlyhigher than the indicator.

According to FIG. 7( a) and FIG. 7( b), by appropriate selection of thepaper weight in gsm and the mixing ratio of burned material of rice huskagainst the entire sheet material, the electromagnetic wave absorbingsheet material targeted a desired frequency band can be produced.

FIG. 8 shows charts indicating the measurement results of theelectromagnetic wave absorption characteristic of the sheet materialproduced by using the burned material of rice bran. FIG. 8( a) shows themeasurement results of the electromagnetic wave absorptioncharacteristic in the case that the paper weight in gsm of burnedmaterial of rice bran is 2000 [g/m²], FIG. 8( b) shows the measurementresults of the electromagnetic wave absorption characteristic in thecase that the paper weight in gsm is 3000 [g/m²].

As shown in FIG. 8( a), in the case that the paper weight in gsm ofburned material of rice bran is 2000 [g/m²], when the mixing ratio ofburned material of rice bran against the entire sheet material is 80[wt. %], the electromagnetic wave absorption with a peak around 5200[MHz] can be confirmed. Since the electromagnetic wave absorption isabout −40 [dB], it is found that the absorption amount is significantlyhigher than the indicator.

As shown in FIG. 8( b), in the case that the paper weight in gsm ofburned material of rice bran is 3000 [g/m²], when the mixing ratio ofburned material of rice husk against the entire sheet material is 60[wt. %], the electromagnetic wave absorption with a peak around 4200[MHz] can be confirmed. Since the electromagnetic wave absorption isabout −28 [dB], it is found that the absorption amount is significantlyhigher than the indicator.

According to FIG. 8( a) and FIG. 8( b), by appropriate selection of thepaper weight in gsm and the mixing ratio of burned material of rice branagainst the entire sheet material, the electromagnetic wave absorbingsheet material targeted a desired frequency band can be produced.

According to FIG. 6 to FIG. 8 explained above, based on the type ofburned plant material used as a material of sheet material, since thefrequency band where the electromagnetic wave absorption becomes a peakis different, it may be selected that what kind of burned plant materialis decided as a material, or, it may be used by mixing them by selectingproperly plural burned plant materials.

In addition, in order to study the conduction characteristic of thesheet material using each of burned material of cacao husk, rice husk,rice bran and soybean hulls, the specific volume resistivity of eachsheet material is measured. In the case of burned material of rice husk,the specific volume resistivity is approx. 10² [Ω·cm] to 10³ [Ω·cm].Furthermore, it is found that the specific volume resistivity hardlychanges by the presence or absence of the pulverization process againstthe burned material of rice husk.

In addition, the specific volume resistivity of each sheet material ismeasured a low resistivity meter (Loresta-GP, MCP-610 manufactured byMitsubishi Chemical Co. Ltd.). More specifically, against any 9 areas ofthe sheet material, by pressing a probe of low resistivity meter, flowscurrent from the probe to the sheet material, the specific volumeresistivity is measured by measuring the potential difference betweenboth sides of sheet material.

In the case of burned material of rice bran, the specific volumeresistivity is approx. 10² [Ω·cm] to 10⁵ [Ω·cm]. In the case of burnedmaterial of soybean hulls, the specific volume resistivity is approx.10¹ [Ω·cm] to 10³ [Ω·cm]. Furthermore, it is found that the specificvolume resistivity hardly changes by the presence or absence of thepulverization process against the burned material of soybean hulls.

The burned material of cacao husk is seen differences in specific volumeresistivity by the presence or absence of the pulverization process, thespecific volume resistivity through the pulverization process is approx.10¹ [Ω·cm] to 10² [Ω·cm], the specific volume resistivity without goingthrough the pulverization process is approx. 10⁰ [Ω·cm] to 10¹ [Ω·cm],it is found that the specific volume resistivity will be increased bythe presence of the pulverization process.

The sheet material of the present embodiment can be suitably used forthe following applications,

(1) Electromagnetic shielding material related to an electronic deviceincluding communication terminal such as a mobile phone and PDA(Personal Digital Assistant), an electronic device such as a microwaveoven, and an electronic substrate used to them,

(2) Electromagnetic shielding material related to an inspectionequipment such as an electronic device (including a shielding box),

(3) Electromagnetic shielding material related to near ETC gate, insidetunnel and inside underground parking lot for suitableintercommunication between vehicles,

(4) Electromagnetic shielding material related to building materialssuch as roof material, floor material or wall material, as well as workshoes, and work clothes,

(5) Electromagnetic shielding material related to cushioning materialcomprising electromagnetic wave absorption effect using a soft stateobject before hot pressing, and further, a helmet used it inside, anautomobile door equipped it inside,

(6) A battery pack cover for a car, and, an undercover for a car.

As a result of this, there are advantageous effects of making itpossible to eliminate a cause for adverse impact on human body from theelectromagnetic waves generated from mobile phones etc. or power cablesetc. around houses, to provide a light-weight shield box, and to providework shoes etc. having anti-static capability.

Furthermore, a soft state object before hot pressing which can be saidas a precursor of the sheet material of the present embodiment can alsobe used. In this case, for example, when it is used as buildingmaterial, it is going to have thermal retaining property, and there isan advantage of being easy to use for clothing.

Then, as a material of the sheet material where both of electromagneticshielding characteristic and electromagnetic wave absorptioncharacteristic are excellent, focusing on cacao husk, the followingmeasurement, etc. were performed.

(1) Component analysis of cacao husk before and after burning,

(2) Tissue observation of cacao husk before and after burning,

(3) Conductivity test for burned material of cacao husk.

FIG. 9( a) shows a chart indicating the result of the component analysisbased on the ZAF quantitative analysis method for cacao husk beforeburning. FIG. 9( b) shows a chart indicating the result of the componentanalysis based on the ZAF quantitative analysis method for cacao huskshown in FIG. 9( a) after burning.

In addition, the results of the component analysis for soybean hulls,rapeseed meal, sesame meal, cotton seed meal, cotton hulls are alsoshown in FIG. 9( a) and FIG. 9( b), for comparison.

Although the production conditions for the burned material of cacao husketc. are as shown in FIG. 1, the “prescribed temperature” and “mediandiameter” were respectively set to 900 [° C.] and approx. 10 μm toapprox. 60 μm. Since it has been said that the ZAF quantitative analysismethod is quantitatively less reliable regarding C, H and N elements incomparison with the organic micro-elemental analysis method, an analysisbased on the organic micro-elemental analysis method is also performedseparately in order to perform a highly reliable analysis regarding C, Hand N elements.

The cacao husk before burning shown in FIG. 9( a) has relatively lowpercentage of “C” and has relatively high percentage of “O”. On theother hand, the cacao husk after burning shown in FIG. 9( b) has averagepercentage of “C” and has low percentage of “O”. Thus, regarding cacaohusk, the increase of “C” can be seen, because the percentage of “C”increases while the percentage of “O” decreases by burning treatment.

FIG. 10( a) shows a chart indicating the result of the componentanalysis based on the organic micro-elemental analysis methodcorresponding to FIG. 9( a). FIG. 10( b) shows a chart indicating theresult of the component analysis based on the organic micro-elementalanalysis method corresponding to FIG. 9( b).

As seen in FIG. 10( a) and FIG. 10( b), the ratios of organic elementsincluded in the burned materials of six kinds of plants can generally beevaluated as similar to each other. However, since rapeseed meal, sesamemeal and cotton seed meal have the common feature of being oil meal, itis perceived that those charts are similar to each other. Specifically,it is perceived that the percentage of “N” is relatively high while theincrease rate in “C” before and after burning is relatively low.

In contrast, since soybean hulls and cotton hulls have the commonfeature of being hulls, it is perceived that those charts are similar toeach other. Specifically, it is perceived that the percentage of “N” isrelatively low while the increase rate in “C” before and after burningis relatively high. On the other hand, a cacao husk has relatively lowpercentage of “C” while has relatively high increase rate in “N” beforeand after burning. In addition, in terms of “C”, cotton hulls is thehighest (approx. 83%), while sesame meal is the lowest (approx. 63%).

In addition, according to the component analysis for the cacao husk, theresults of the component analysis (organic micro-elemental analysis) ofcacao husk before burning had the carbon component, hydrogen componentand nitrogen component of respectively approx. 43.60%, approx. 6.02% andapprox. 2.78%. In contrast, the results of the component analysis(organic micro-elemental analysis) of cacao husk after burning had thecarbon component, hydrogen component and nitrogen component ofrespectively approx. 65.57%, approx. 1.12% and approx. 1.93%.Furthermore, the specific volume resistivity of the burned material ofcacao husk was 4.06×10⁻¹² Ω·cm.

Furthermore, according to the component analysis based on the organicmicro-elemental analysis method, it is perceived that the cacao husketc. before burning, in general, are essentially rich in the carboncomponent. In contrast, it is perceived that, regarding cacao husk etc.after burning, the carbon percentage is increased by burning.

FIG. 11 shows a chart indicating the test results of the conductivitytest regarding the burned material of cacao husk after pulverization.The lateral axis and vertical axis of FIG. 11 respectively represent thepressure [MPa] applied to the burned material of cacao husk and thespecific volume resistivity [Ω·cm]. In addition, the test results forcotton hulls, sesame meal, rapeseed meal, cotton seed meals are alsoshown in FIG. 11, for reference.

The method employed is that, 1 g of the powdered “burned material ofcacao husk” as a test object is put in a cylindrical container with aninner diameter of approx. 25Φ, and a cylindrical brass with a diameterof approx. 25Φ is aligned to the opening part of the above container,and then a press machine (MP-SC manufactured by Toyo Seiki Seisaku-Sho,Ltd.) is used to apply pressure to the burned material of cacao husk bypressing via the brass from 0 [MPa] to 4 [MPa] or 5 [MPa] with anincrement of 0.5 [MPa] so that the specific volume resistivity ismeasured by bringing the side part and bottom part of the brass intocontact with a probe of a low resistivity meter (Loresta-GP MCP-T600manufactured by Mitsubishi Chemical Co. Ltd.) while the burned materialof cacao husk is pressured.

When a cylindrical container with approx. 10Φ was used instead of thecylindrical container with approx. 25Φ, and a cylindrical brass with adiameter of approx. 10Φ was used instead of the cylindrical brass with adiameter of approx. 25Φ, and when the rest of the conditions were thesame as above, an equivalent test result was obtained by theconductivity test.

According to the test result shown in FIG. 11, it is found that theburned material of cacao husk has a characteristic which reduces itsspecific volume resistivity (that is, increasing the conductivity) byapplying a pressure of 0.5 [MPa] or above, for example, and as thepressure increases.

The specific volume resistivity of cotton hulls is 3.74×10⁻² [Ω·cm], thespecific volume resistivity of sesame meal is 4.17×10⁻² [Ω·cm], thespecific volume resistivity of rapeseed meal is 4.49×10⁻² [Ω·cm], thespecific volume resistivity of cotton seed meals is 3.35×10⁻² [Ω·cm] andthe specific volume resistivity of cacao husk is 4.06×10⁻² [Ω·cm].

In fact, although there is exactly three times difference, for example,between the specific volume resistivity of 1.00×10⁻¹ [Ω·cm] and thespecific volume resistivity of 3.00×10⁻¹ [Ω·cm], such a degree ofexactness is not required in the measurement results of the specificvolume resistivity as it is clearly known by those skilled in the art.Thus, since the specific volume resistivity of 1.00×10⁻¹ [Ω·cm] and thespecific volume resistivity 3.00×10⁻¹ [Ω·cm] both are on the same orderof “10⁻¹”, please note that those can be evaluated as equivalent to eachother.

FIG. 12 shows a chart indicating the relationship between the contentratio of the burned material of cacao husk kneaded into ethylenepropylene diene terpolymer and the specific volume resistivity. That is,in this case, as a comparative example of the sheet material, the thingkneaded the burned material of cacao husk into ethylene propylene dieneterpolymer is produced. The lateral axis and vertical axis of FIG. 12respectively represent the content ratio [phr] of the burned material ofcacao husk and the specific volume resistivity [Ω·cm]. In addition, forcomparison, FIG. 12 also shows those of the electromagnetic shieldingmember using the respective burned materials of cotton hulls, sesamemeal, rapeseed meal and cotton seed meals. The plotted numeric in FIG.12 is an average of measurements at 9 arbitrarily chosen points in theelectromagnetic shielding member (same applies hereinafter).

As shown in FIG. 12, each specific volume resistivity of cacao husk etc.had a measurement result similar to each other. Each specific volumeresistivity of cacao husk etc. is also similar to the specific volumeresistivity of soybean hulls.

Regarding only to the respective burned materials of soybean hulls,rapeseed meal, sesame meal, cotton seed meal and cotton hulls, when thecontent ratio of the burned plant material against rubber is set to 200[phr] or above, it is found that the specific volume resistivitysignificantly decreases in all cases in contrast to the case that saidcontent ratio is set to 150 [phr] or below. In contrast, regarding theburned materials of cacao husk, it is found that the specific volumeresistivity significantly decreases linearly to the increase of thecontent ratio against the rubber.

Regarding the burned materials of cacao husk etc. according to thisembodiment, the bulk specific gravity has been measured in conformity toJIS K-1474. The bulk specific gravity of rapeseed meal, sesame meal,cotton seed meal, cotton hulls and cacao husk were approx. 0.6 g/ml to0.9 g/ml, approx. 0.7 g/ml to 0.9 g/ml, approx. 0.6 g/ml to 0.9 g/ml,approx. 0.3 g/ml to 0.5 g/ml, and approx. 0.3 g/ml to 0.5 g/mlrespectively. The kinds of hulls (cotton hulls and cacao husk) are arelatively bulky.

FIG. 13 and FIG. 14 show SEM pictures of cacao husk before burning. FIG.13( a), FIG. 13( b), FIG. 14( a), and FIG. 14( b) respectively show apicture of the outer skin taken at 350-fold magnification, a picture ofthe inner skin taken at 100-fold magnification, a picture of the innerskin taken at 750-fold magnification, and a picture of the inner skintaken at 1500-fold magnification.

As shown in FIG. 13( a), the outer skin of cacao husk before burning isa form like the surface of a limestone. In contrast, as shown in FIG.13( b), the inner skin of cacao husk before burning is a form like thefibrous.

Interestingly, as shown in FIG. 14( a) and FIG. 14( b), the inner skinof cacao husk before burning is equipped with spiral portion when thefibrous part is expanded. In addition, the diameter of spiral portion isvisible to 10 μm to 20 μm in general.

FIG. 15 and FIG. 16 show SEM pictures of cacao husk burned withoutdistinguishing by the inner skin and the outer skin. FIG. 15( a), FIG.15( b), and FIG. 16( a) respectively show a picture of the burnedmaterial taken at 1500-fold magnification, and FIG. 16( b) shows apicture of the burned material taken at 3500-fold magnification.

From FIG. 15( a) and FIG. 16( b), it is confirmed that the fibrousportion looked at the inner skin of cacao husk before burning isremaining also in the burned material of cacao husk. In addition, as forthe size of the burned material, the diameter of spiral portion seems tobe shrunk to approximately 5 μm to 10 μm. Moreover, from FIG. 15( b) andFIG. 16( a), it is confirmed that the burned material of cacao husk is avariegated porous structure.

The spiral portion is not confirmed in soybean hulls, rapeseed meal,sesame meal, cotton seed meal, cotton hulls and soybean chaffs as statedabove. Therefore, such a form has a high possibility of being peculiarto a cacao husk. On the other hand, since the conduit side wall portionetc. of seed plant, such as lotus roots and pumpkins, further, the innerskin of peanuts etc. also contain a spiral portion, the effect which isobtained in the case using the burned material of cacao husk can beexpected. From this, the scope of the present invention is intended toinclude those using any burned plant material containing a spiralportion.

Here, when a pulverization treatment is performed against the burnedmaterial of cacao husk, or it is kneaded into rubber, there is apossibility that the spiral portion may be crushed. And, when comparingthe electromagnetic shielding characteristic of the sheet materialthrough the pulverization treatment of the burned material of cacao huskshown in FIG. 2 and the electromagnetic shielding characteristic of thesheet material without going through the pulverization treatment shownin FIG. 3, there is a significant difference in the electromagneticshielding effectiveness. On the other hand, when comparing FIG. 4 andFIG. 5 showing the electromagnetic shielding characteristic according tothe burned material of soybean hulls, there is no much difference in theelectromagnetic shielding effectiveness.

From this, it can be considered that the spiral portion found in theburned material of cacao husk contributes to convert the electromagneticwave energy into other energy efficiently. As in the present embodiment,without performing the pulverization treatment against the burnedmaterial of cacao husk, the sheet material using the wet-process sheetproduction method which can produce while leaving well the spiralportion can be obtained excellent electrical properties that rubbermaterial would not be obtained. Saying in addition, the sheet materialusing the wet-process sheet production method has the advantage whichcan leave own structure of each of the burned plant material.

Embodiment 2

Although the sheet material using the burned material of cacao husk hasbeen explained mainly in Embodiment 1 of the present invention, a sheetmaterial added the stainless fiber which is a metal filler againstvarious burned plant materials will be explained in Embodiment 2 of thepresent invention. In addition, a stainless fiber is an example of ametal filler, and a metal filler which can be used in the sheet materialof the present embodiment is not limited to a stainless fiber.

Incidentally, the stainless fiber used in the present embodiment isNaslon (registered trademark) CHOP6 manufactured by Nippon Seisen Co.,Ltd., except that the stainless fiber is mixed together at the time ofmixture of burned plant material and aramid fiber, the production methodof sheet material of the present embodiment is the same as that ofEmbodiment 1. In addition, the burning temperature of each burned plantmaterial is set to 900 [° C.].

TABLE 1 Category 1st category 2nd category 3rd category BurnedPulverized powder 50 wt. % Pulverized powder 25 wt. % Pulverized powdercarbon RBC, RHC, SHC RBC, RHC, SHC (150~250 μm) No pulverized piece Nopulverized piece 37.5 25.0 12.5   0 wt. % RHC-L, SHC-L RHC-L, SHC-L SUSfiber 0 25 12.5 25.0 37.5 50.0 wt. % Paper weight 2000 [g/m²]

TABLE 2 4th category Composition CHC-L SUS fiber SUS fiber + CHC-L(product name) formed sheet formed sheet formed sheet Burned carbonCHC-L 50 wt. % 0 CHC-L 25 wt. % SUS fiber 0 50 wt. % 25 wt. %

Table 1 and Table 2 are tables showing the configuration of the sheetmaterial according to Embodiment 2 of the present invention. As shown inTable 1 and Table 2, the configuration of the sheet material of thepresent embodiment is roughly divided into 4 categories.

As for 1^(st) category, the thing which the mixing ratio of each of thefollowings against the entire sheet material is 50 [wt. %] is prepared.That is, the sheet material according to 1^(st) category is a sheetmaterial which is not mixed with stainless (SUS) fiber against theabove-mentioned various burned plant materials.

Burned material of rice bran performed pulverization treatment (RBC),and

Burned material of rice husk performed pulverization treatment (RHC),and

Burned material of soybean hulls performed pulverization treatment(SHC), and

Burned material of rice husk without performing pulverization treatment(RHC-L), and

Burned material of soybean hulls without performing pulverizationtreatment (SHC-L).

As for 2^(nd) category, the thing which the mixing ratio of each of thefollowings against the entire sheet material is 25 [wt. %] and themixing ratio of stainless (SUS) fiber against the entire sheet materialis 25 [wt. %] is prepared. That is, the sheet material according to2^(nd) category is a sheet material which is mixed with stainless (SUS)fiber against the various burned plant materials.

Burned material of rice bran performed pulverization treatment (RBC),and

Burned material of rice husk performed pulverization treatment (RHC),and

Burned material of soybean hulls performed pulverization treatment(SHC), and

Burned material of rice husk without performing pulverization treatment(RHC-L), and

Burned material of soybean hulls without performing pulverizationtreatment (SHC-L)

As for 3^(rd) category, the things which the mixing ratios of the burnedmaterial of cacao husk performed the pulverization treatment under thecondition to fit the size of 150 [μm] to 200 [μm] majority (CHC) and thestainless (SUS) fiber against the entire sheet material are respectively37.5 [wt. %] and 12.5 [wt. %], 25 [wt. %] and 25 [wt. %], 12.5 [wt. %]and 37.5 [wt. %], 0 [wt. %] and 50.0 [wt. %] are prepared. That is, thesheet material according to 3^(rd) category is a sheet material whichstainless (SUS) fiber is selectively mixed against the burned materialof cacao husk performed the pulverization treatment.

As for 4^(th) category, the things which the mixing ratios of the burnedmaterial of cacao husk without performing the pulverization treatment(CHC-L) and the stainless (SUS) fiber against the entire sheet materialare respectively 50.0 [wt. %] and 0 [wt. %], 0 [wt. %] and 50 [wt. %],25 [wt. %] and 25 [wt. %] are prepared. That is, the sheet materialaccording to 4^(th) category is a sheet material which stainless (SUS)fiber is selectively mixed against the burned material of cacao huskwithout performing the pulverization treatment.

Incidentally, as for those belonging to any of 1^(st) category to 4^(th)category, the paper weight in gsm is set to 2000 [g/m²].

FIG. 17 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material accordingto 1^(st) category, that is, the sheet material is not mixed withstainless (SUS) fiber against various burned plant material. Thismeasurement has been performed by KEC method, the lateral axis andvertical axis of FIG. 17( a) respectively represent the frequency [MHz]and the electric field shielding effectiveness [dB]. Further, thelateral axis and vertical axis of FIG. 17( b) respectively represent thefrequency [MHz] and the magnetic field shielding effectiveness [dB].

According to FIG. 17( a), the sheet material which has the highestelectric field shielding effectiveness is produced by mixing 50 [wt. %]burned material of soybean hulls without performing pulverizationtreatment (SHC-L), and, the highest electric field shieldingeffectiveness is a value of approx. 20 [dB] or above up to about 1000[MHz].

Then, the sheet material produced by mixing 50 [wt. %] burned materialof rice husk without performing pulverization treatment (RHC-L) and thesheet material produced by mixing 50 [wt. %] burned material of soybeanhulls performed pulverization treatment (SHC) are approximately the samevalue, the electric field shielding effectiveness is a value of approx.7 [dB] or above up to frequencies of about 1000 [MHz].

In addition, the sheet material produced by mixing 50 [wt. %] burnedmaterial of rice bran performed pulverization treatment (RBC) and thesheet material produced by mixing 50 [wt. %] burned material of ricehusk performed pulverization treatment (RHC) are approximately the samevalue, the electric field shielding effectiveness is a value of approx.5 [dB] or above up to frequencies of about 1000 [MHz].

On the other hand, according to FIG. 17( b), in any sheet material,excellent value as the magnetic field shielding effectiveness is notobtained.

FIG. 18 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material accordingto 2^(nd) category. That is, the sheet material is mixed with stainless(SUS) fiber against various burned plant material. FIG. 18 iscorresponding to FIG. 17.

As apparent from FIG. 18( a), when compared to FIG. 17( a), generally,it is found that the electric field shielding effectiveness is improved.Except for the mixture which the burned material of rice bran performedpulverization treatment (RBC) and the stainless (SUS) fiber are at 25[wt. %] each, and the mixture which the burned material of rice huskperformed pulverization treatment (RHC) and the stainless (SUS) fiberare at 25 [wt. %] each, the electric field shielding effectiveness is avalue of approx. 58 [dB] or above up to frequencies of about 1000 [MHz],and in the low frequency range 50 [MHz] or below, the electric fieldshielding effectiveness of 80 [dB] to 100 [dB] at the maximum isobtained.

In addition, in the mixture that the burned material of rice huskperformed pulverization treatment (RHC) and the stainless (SUS) fiberare at 25 [wt. %] each, the electric field shielding effectiveness is avalue of approx. 50 [dB] or above up to frequencies of about 1000 [MHz],and in the mixture that the burned material of rice bran performedpulverization treatment (RBC) and the stainless (SUS) fiber are at 25[wt. %] each, the electric field shielding effectiveness is a value ofapprox. 40 [dB] or above on average up to frequencies of about 1000[MHz], and is approx. 30 [dB] as the minimum value.

Here, in the battery pack cover for a car and the undercover for a car,in general, in the frequency band of 100 [MHz] to 2 [GHz], the electricfield shielding effectiveness approx. 60 [dB] or above is required.Therefore, in the sheet material according to FIG. 18( a), except forthe mixture that the burned material of rice bran performedpulverization treatment (RBC) and the stainless (SUS) fiber are at 25[wt. %] each, and the mixture that the burned material of rice huskperformed pulverization treatment (RHC) and the stainless (SUS) fiberare at 25 [wt. %] each, they can be used as the battery pack cover for acar, etc.

In addition, the conventional battery pack cover for a car is necessarytroublesome production process to cover entire battery pack cover for acar, mainly by using stainless material as a mesh. However, the batterypack cover using the sheet material of the present embodiment ispossible to adopt a simplified production method to mold integrally byprepare a metal mold, etc. in accordance with the shape, size of batterypack for a car. Also, the battery pack cover using the sheet material ofthe present embodiment, as a result containing burned plant material, itis also possible to achieve weight reduction compared to conventionalbattery pack cover for a car since the ratio of stainless material canbe reduced relatively.

Furthermore, generally, since the stainless material used inconventional battery pack for a car is expensive compared to the burnedplant material, there is the advantage that the battery pack cover for acar mixed with burned plant material becomes inexpensive

See FIG. 18( b), compared to FIG. 17( b), generally, it is found thatthe magnetic field shielding effectiveness is improved. In addition,from FIG. 18( a) and FIG. 18( b), it is found that there is an affinityfor the electric field shielding effectiveness and the magnetic fieldshielding effectiveness. That is, for the mixture which the burnedmaterial of rice husk performed pulverization treatment (RHC) and thestainless (SUS) fiber are at 25 [wt. %] each, the magnetic fieldshielding effectiveness and the electric field shielding effectivenessare slightly less than the others, and for the mixture which the burnedmaterial of rice bran performed pulverization treatment (RBC) and thestainless (SUS) fiber are at 25 [wt. %] each, the magnetic fieldshielding effectiveness and the electric field shielding effectivenessare slightly less than the others further.

FIG. 19 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material accordingto 3^(rd) category. That is, the sheet material is selectively mixedwith stainless (SUS) fiber against burned material of cacao huskperformed pulverization treatment. FIG. 19 is corresponding to FIG. 17.

As apparent from FIG. 19( a), compared to FIG. 17( a), generally, it isfound that the electric field shielding effectiveness is improved. Inaddition, please note that the graph at the bottom in FIG. 19( a) isalso shown in FIG. 17( a).

See FIG. 19( a), if the mixing ratio of stainless (SUS) fiber isincreased more, the electric field shielding effectiveness is improvedmore. Even if the mixing ratios of the burned material of cacao huskperformed pulverization treatment (CHC) and the stainless (SUS) fiberagainst the entire sheet material are respectively 12.5 [wt. %] and 37.5[wt. %], the electric field shielding effectiveness of 60 [dB] or aboverequired for above-described battery pack cover for a car, etc. can beachieved.

See FIG. 19( b), compared to FIG. 17( b), generally, it is found thatthe magnetic field shielding effectiveness is improved. In addition,from FIG. 19( a) and FIG. 19( b), it is found that there is an affinityfor the electric field shielding effectiveness and the magnetic fieldshielding effectiveness.

In addition, the things which the mixing ratios of the burned materialof cacao husk and the stainless (SUS) fiber against the entire sheetmaterial are respectively 10 [wt. %], 30 [wt. %], 50 [wt. %], and themixing ratio of the burned material of cacao husk and the stainless(SUS) fiber is 1;1, and the thing that the mixing ratio of the burnedmaterial of cacao husk against the entire sheet material is 50 [wt. %](no SUS fiber) are respectively produced, and the electromagneticshielding effectiveness is measured by dual focus flat cavity (DFFC)method in addition to KEC method.

As a result, in the case of KEC method, the thing of “10 [wt. %]” isapprox. 45 [dB] on average, the thing of “30 [wt. %]” is approx. 80 [dB]on average, the thing of “50 [wt. %]” is approx. 105 [dB] on average,the thing of “50 [wt. %] (no SUS fiber)” is approx. 30 [dB] on averageas the electric field shielding effectiveness.

In addition, DFFC method, although it is measured in the range of 1[MHz] to 9 [MHz], the thing of “10 [wt. %]” is approx. 40 [dB] onaverage, the thing of “30 [wt. %]” is approx. 75 [dB] on average, thething of “50 [wt. %]” is approx. 95 [dB] on average, the thing of “50[wt. %] (no SUS fiber)” is approx. 20 [dB] on average as theelectromagnetic shielding effectiveness.

FIG. 20 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material accordingto 4^(th) category. That is, the sheet material is selectively mixedwith stainless (SUS) fiber against burned material of cacao husk withoutperforming the pulverization treatment. FIG. 20 is corresponding to FIG.17.

As apparent from FIG. 20( a), compared to FIG. 17( a), generally, it isfound that the electric field shielding effectiveness is improved.Surprisingly, even if the stainless (SUS) fiber is not mixed completely,it was 30 [dB] or above in the frequency band up to 1000 [MHz].

Furthermore, surprisingly, the electric field shielding effectiveness ofthe mixture of the burned material of cacao husk without performing thepulverization treatment and the stainless (SUS) fiber is more increasedthan that of the single substance of stainless (SUS) fiber. Therefore,for example, when such a sheet material is used as an inspectionequipment such as an electronic device, near ETC gate, buildingmaterials such as a roof material, a floor material or a wall material,work shoes, work clothes, a helmet, and a battery pack cover for a car,the excellent effect such as lightweight and inexpensive, and moreover,realization of simplified production process can be achieved.

See FIG. 20( b), compared to FIG. 17( b), generally, it is found thatthe magnetic field shielding effectiveness is improved. In addition,from FIG. 20( a) and FIG. 20( b), it is found that there is an affinityfor the electric field shielding effectiveness and the magnetic fieldshielding effectiveness.

As described above, in the present embodiment, although the explanationof the measuring result based on KEC method is mainly performed, asdescribed in Embodiment 1, when the electromagnetic shieldingcharacteristic of sheet material based on Advantest method is measured,it is confirmed that similar result can be obtained.

FIG. 23 is a figure showing the electromagnetic shielding characteristicof the sheet material consisting of the mixture of the burned plantmaterial of the present embodiment and SUS fiber measured based on thearch test method. The lateral axis and vertical axis of FIG. 23respectively represent the frequency [MHz] and the electromagneticshielding effectiveness [dB].

In this case, for comparison, the electromagnetic shieldingcharacteristic for the laminate consisting of the sheet materialproduced from a single substance of stainless (SUS) fiber and the sheetmaterial produced from a single substance of burned plant material isalso studied. In addition, the things which the mixing ratios of theburned material of cacao husk and the SUS fiber against the entire sheetmaterial are respectively 10 [wt. %], 30 [wt. %], 50 [wt. %], and themixing ratio of the burned material of cacao husk and the SUS fiber is1;1, and the thing which the mixing ratio of the burned material ofcacao husk against the entire sheet material is 50 [wt. %] (no SUSfiber) are respectively produced.

According to FIG. 23, it is found that the electromagnetic shieldingcharacteristic of the sheet material of the present embodiment isobtained high electromagnetic shielding effectiveness 40 [dB] or aboveat around 100 [MHz] and at around 1000 [MHz] without depending on themixing ratio of the burned material of cacao husk and the SUS fiberagainst the entire sheet material. Therefore, if there is a request ofsheet material which is excellent electromagnetic shieldingeffectiveness, the burned material of cacao husk is not required so manymixed amount.

FIG. 24 is a figure showing the electromagnetic shielding characteristicfor the laminate consisting of the sheet material produced from a singlesubstance of SUS fiber and the sheet material produced from a singlesubstance of burned plant material measured based on the arch testmethod as a comparative example. The lateral axis and vertical axis ofFIG. 24 respectively represent the frequency [MHz] and theelectromagnetic shielding effectiveness [dB].

As shown in FIG. 24, in the frequency 1000 [MHz] or below, it is foundthat the electromagnetic shielding effectiveness can be realized approx.30 [dB] as an average.

However, as obvious when comparing with FIG. 23, in the case of thesheet material of the comparative example, the electromagnetic shieldingeffectiveness more than 40 [dB] is confirmed only around 100 [MHz], itis less than 30 [dB] around 1000 [MHz].

To summarize the above, by comparing FIG. 23 and FIG. 24, regarding thesheet material, it can be seen that the electromagnetic shieldingeffectiveness of those mixed the burned plant material and the SUS fiberat the time of producing is increased more than that of those laminatedsimply ones produced from a single substance of burned plant materialand ones produced from a single substance of SUS fiber. In other word,the sheet material of the present embodiment can obtain excellentelectromagnetic shielding effectiveness since it is produced in a statein which the burned plant material and the SUS fiber are mixed.

Furthermore, the sheet material of the present embodiment can besuitably used for an electromagnetic shielding member. More specially,it is possible to produce the electromagnetic shielding member which islaminated so that the sheet material formed by mixing of the burnedplant material and SUS fiber is outside and the sheet material producedfrom a single substance of burned plant material is inside. In addition,a insulating layer, optionally, may be provided on the surface of theouter sheet material. In this way, by covering an electromagnetic wavesource with an electromagnetic shielding member, it becomes possiblethat an electromagnetic wave from the electromagnetic wave source doesnot leak to the outside. In such case, since the inner sheet materialmainly contributes to the electric field absorption and the outer sheetmaterial mainly contributes to the magnetic field shielding, theelectromagnetic wave in the electromagnetic shielding member can bereduced. Furthermore, when the insulating layer is provided, it can beprevented that the electromagnetic wave which could not be shielded byeach of the sheet material is irradiated to the outside of theelectromagnetic shielding member. As an example of the use of this kindof electromagnetic shielding member, above-described inspectionequipment such as electronic device, battery pack cover for a car, etc.can be mentioned.

In addition, the above-mentioned each sheet material can also bereversed. That is, it is possible to produce the electromagneticshielding member which is laminated so that the sheet material formed bymixing the burned plant material and SUS fiber is inside and the sheetmaterial produced from a single substance of burned plant material isoutside. In this way, by covering a prevention object of electromagneticwave irradiation with an electromagnetic shielding member, it can beavoided that electromagnetic waves from the electromagnetic wave sourcelocated outside is irradiated to the prevention object. In this case,since the outer sheet material mainly contributes to the electric fieldadsorption, the electromagnetic shielding member not only has merely anelectromagnetic shielding function but also it is possible to avoid anadverse effect to the electronic device, etc. located around theelectromagnetic shielding member. As an example of the use of this kindof electromagnetic shielding member, above-described building material,clothing, etc. can be mentioned.

Embodiment 3

In Embodiment 3 of the present invention, at the time of the pressingprocess which is performed during the production of sheet material, thepressurizing conditions are changed.

TABLE 3 Composition Cacao husk formed sheet SUS fiber + Cacao huskformed sheet Cacao husk 10 30 50 5 15 25 (150-250 μm) SUS fiber 0 5 1525 Paper weight 2000 [g/mm²] Pressurization low p high p low p high plow p high p low p high p low p high p low p high p Bulk density 0.861.01 0.8 1.07 0.71 1.09 0.84 1.04 0.77 1.22 0.58 1.37 [g/cm3] Thickness[mm] 2.4 2 2.6 1.9 2.9 1.9 2.4 1.8 2.7 1.6 3.3 1.4

Table 3 shows the relationship between the bulk density and thethickness of the sheet material which is produced by performing apressurization of about 3 MPa and the sheet material which is producedby performing a pressurization of about 10 MPa during the pressingprocess which is performed after passing through the wet-process sheetproduction process and the drying process. In addition, as for thereason of “about 10 MPa”, it is because this value is thepress-pressurizing value for the close packing.

The production method of the sheet material of the present embodiment isthe same as that of Embodiment 1 except for the pressurizing condition,the burning temperature of each burned plant material is set to 900 [°C.]. In addition, in the present embodiment, it will be explained aboutthe sheet material which is produced by the addition of stainless fiberselectively against burned material of cacao husk without performing thepulverization treatment.

As shown in Table 3, in the case of no addition of stainless fiber, themixing ratios of the burned material of cacao husk without performingthe pulverization treatment against the entire sheet material arerespectively 10 [wt. %], 30 [wt. %] and 50 [wt. %].

On the other hand, in the case of addition of stainless fiber, themixing ratios of the burned material of cacao husk without performingthe pulverization treatment and the stainless fiber against the entiresheet material are respectively 10 [wt. %], 30 [wt. %] and 50 [wt. %].

Against the above 6 patterns samples, when the pressurization isperformed at about 3 MPa and when the pressurization is performed atabout 10 MPa, in both cases, the bulk density is increased more at thepressurization of about 10 MPa. In addition, along with this, thethickness of sheet material is also reduced. For the specific numericalvalues of bulk density and thickness of the sheet material, refer toTable 3.

FIG. 21 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material withoutaddition of stainless fiber against burned material of cacao huskwithout performing the pulverization treatment. This measurement isperformed by KEC method, the lateral axis and vertical axis of FIG. 21(a) respectively represent the frequency [MHz] and the electric fieldshielding effectiveness [dB]. In addition, the lateral axis and verticalaxis of FIG. 21( b) respectively represent the frequency [MHz] and themagnetic field shielding effectiveness [dB]. Further, “high p” in FIG.21 means that the pressurization in Table 3 is “high”, and “low p” meansthat the pressurization in Table 3 is “low”.

According to FIG. 21( a), in the case of no addition of stainless fiber,with increasing the mixing ratio of burned material of cacao huskwithout performing the pulverization treatment against the sheetmaterial, the electric field shielding effectiveness is increased byperforming the high pressurization. However, in the case that the mixingratio of burned material of cacao husk without performing thepulverization treatment is 10 [wt. %], the clear difference of electricfield shielding effectiveness by the high and low of pressurization isnot observed.

According to FIG. 21( b), the clear difference of magnetic fieldshielding effectiveness by the high and low of mixing ratio of burnedmaterial of cacao husk without performing the pulverization treatmentand by the high and low of pressurization is not observed.

When the bulk density is increased, since the distance between powder ofburned material of cacao husk is shortened, since the powder of burnedmaterial of cacao husk and the stainless fiber come into contact, andsince the distance between stainless fibers is shortened, as the resultthat the electrical conductivity is increased, the electric fieldshielding property of sheet material is improved. In addition, evenafter performing a pressurization of 10 MPa, since a space is remaininginside of sheet material, the possibility that the spiral structure isdestroyed is small.

Furthermore, when attention is paid to the lower limit value of bulkdensity, although the bulk density is about 0.3 [g/cm³] during the papermaking process which is the production process of sheet material, inorder to prevent the detachment of powder of burned material of cacaohusk, once melted the surface of sheet material, the bulk densitybecomes about 0.5 [g/cm³]. In other word, the sheet material of thepresent embodiment may be pressurized under conditions that the bulkdensity becomes about 0.5 [g/cm³] at least.

FIG. 22 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material withaddition of stainless fiber against burned material of cacao huskwithout performing the pulverization treatment, it is corresponding toFIG. 21.

According to FIG. 22( a), in the case of addition of stainless fiber,with increasing the mixing ratio of burned material of cacao huskwithout performing the pulverization treatment, the electric fieldshielding effectiveness is increased by performing the highpressurization. However, in the case that the mixing ratio of burnedmaterial of cacao husk without performing the pulverization treatment is10 [wt. %], the clear difference of electric field shieldingeffectiveness by the high and low of pressurization is not observed. Onthe other hand, in the case of the best condition, the electric fieldshielding effectiveness more than 100 [dB] or approaching to 120 [dB] isobtained.

According to FIG. 22( b), in the case of addition of stainless fiberagainst burned material of cacao husk without performing thepulverization treatment, with increasing the mixing ratio of burnedmaterial of cacao husk without performing the pulverization treatment,the electric field shielding effectiveness is increased by performingthe high pressurization. In particular, the electric field shieldingeffectiveness is increased dramatically compared to those shown in FIG.17( b) and FIG. 18( b).

As described above, summarizing the various measurement results, thesheet materials of Embodiment 2 and 3 are the following properties.

(1) For the sheet material using the mixture of SUS fiber and burnedplant material, the electromagnetic shielding effectiveness is increasedmore if the ratio of SUS fiber is increased more, however the cost isincreased. At market prices, the cost of SUS fiber is about 5 to 6 timesof the cost of burned plant material. Thus, although the electric fieldshielding effectiveness required by applications of the sheet materialis not necessarily constant, for the mixture of SUS fiber and burnedplant material, 1:3 to 3:1 is generally good.

(2) If the mixing ratio of SUS fiber and burned plant material againstthe sheet material is increased more, the electromagnetic shieldingeffectiveness of sheet material is increased more.

(3) Without increasing the mixing ratio of SUS fiber and burned plantmaterial against the sheet material, if the bulk density is increased bypressurization during the production of the sheet material, theelectromagnetic shielding effectiveness of sheet material is increased.

Embodiment 4

In Embodiment 1, although an example that the cacao husk after burningis pulverized then is introduced in an agitated vessel with propellerimpeller is explained, in this embodiment, a sheet material produced bythe process that the cacao husk before burning is pulverized, afterthat, is performed burning treatment is explained. In addition, as amill, general-purpose cutter mill is used.

FIG. 25 is a figure showing the measurement results of the specificvolume resistivity of the sheet material consisting of cacao husk whichis burned after performing the pulverization process. This measurementis performed by using a low resistivity meter (Loresta-GP, MCP-610manufactured by Mitsubishi Chemical Co. Ltd.). The measurement objectsof the specific volume resistivity are both of the sheet material usedthose that passed through a mesh of a 500 μm by 500 μm wire mesh, etc.(plotted by Δ), and the sheet material used those that did not passthrough it (plotted by ∇). In addition, for reference, FIG. 25 alsoshows the specific volume resistivity of the sheet material produced bythe process in FIG. 1 (however, without performing the pulverizationprocess), (plotted by □).

First, in the case of the sheet material used those that passed throughthe mesh, there is no significant change in the specific volumeresistivity even compared with the sheet material produced by theprocess in FIG. 1 (however, without performing the pulverizationprocess), In either case, it is considered due to the relatively smallspiral portion of the cacao husk occupied in the sheet material.

On the other hand, in the case of the sheet material used those that didnot pass through the mesh, a decrease of one or two orders is seen inthe specific volume resistivity. Since the cacao husk which did not passthrough the mesh contains relatively many spiral portion, it isconsidered due to said portion.

Therefore, in the field that low specific volume resistivity isrequired, the sheet material consisting of the cacao husk which does notpass through the mesh, that is, the cacao husk which contains relativelymany spiral portion may be used.

Embodiment 5

Next, the sheet material which is mixed various matrices at the time ofproduction is explained. In this case, in addition to measuring theconduction characteristic and the electromagnetic shieldingcharacteristic of the sheet material of 80 mm square produced usingpolypropylene (PP), high molecular polyethylene (HDPE) as a matrix andglass fiber (GF) as a fibrous material, the tensile test is performed.Specific production conditions of the sheet material are as follows. Inaddition, for comparison, following Sheet material 5 does not contain amatrix.

Sheet material 1 (thickness t=1.5 mm)

SUS fiber: 15 wt. %

Cacao husk (150 μm or below): 15 wt. %

Polyethylene fiber: 60 wt. %

GF (glass fiber): 10 wt. %

Paper weight in gsm: 2000 g/m²

Sheet material 2 (thickness t=b 1.4 mm)

SUS fiber: 15 wt. %

Cacao husk (150 μm or below): 15 wt. %

Polyethylene fiber: 40 wt. %

GF (glass fiber): 30 wt. %

Paper weight in gsm: 2000 g/m²

Sheet material 3 (thickness t=1.6 mm)

SUS fiber: 15 wt. %

Cacao husk (150 μm or below): 15 wt. %

PP (polypropylene): 60 wt. %

Aramid fiber: 10 wt. %

Paper weight in gsm: 2000 g/m²

Sheet material 4 (thickness t=1.6 mm)

SUS fiber: 15 wt. %

Cacao husk (150 μm or below): 15 wt. %

HDPE (high density polyethylene): 60 wt. %

Aramid fiber: 10 wt. %

Paper weight in gsm: 2000 g/m²

Sheet material 5 (thickness t=1.6 mm)

SUS fiber: 15 wt. %

Cacao husk (150 μm or below): 15 wt. %

Matrix: None

Polyethylene fiber: 60 wt. %

Aramid fiber: 10 wt. %

Paper weight in gsm: 2000 g/m²

FIG. 26 is a figure showing the specific volume resistivity of Sheetmaterial 1 to Sheet material 5. According to FIG. 26, although thechange based on the presence or absence of matrix and the type is notseen much, nevertheless, Sheet material 1 and 2 including glass fiber asa matrix show slightly low specific volume resistivity compared toothers.

For reference, the average values of the specific volume resistivity ofSheet material 1 to Sheet material 5 are respectively 5.96×10⁻² Ω·cm,4.90×10⁻² Ω·cm, 2.00×10⁻¹ Ω·cm, 1.57×10⁻¹ Ω·cm and 1.16×10⁻¹ Ω·cm.

FIG. 27 is a figure showing the electromagnetic shielding effectivenessof Sheet material 1 to Sheet material 5. As shown in FIG. 27, theelectromagnetic shielding effectiveness of Sheet material 1 to Sheetmaterial 5 is almost the same value 1000 [MHz] or below, even include aparticular matrix, the difference between others is not seen.

FIG. 28 is a schematic diagram of workpiece for tensile test of Sheetmaterial 1 to Sheet material 5. As shown in FIG. 28, this workpiece hasthe conditions that the central portion is about 6.0 mm in width, thelength is 35.0 mm and the both ends are sufficient area. The tests oftensile strength [MPa] and tensile elasticity [MPa] are performed byusing these workpieces.

FIG. 29 is a figure showing the test results of tensile test of Sheetmaterial 1 to Sheet material 5. The lateral axis and vertical axis ofFIG. 29 respectively represent the strain and the stress. First,focusing on the length of each graph in FIG. 29, the graph length ofSheet material 5 is significantly longer as compared to the graph lengthof the other sheet material. From this, when the matrix is mixed, it isfound that the fracture ductility is reduced. In addition, it is foundthat the graph length of Sheet material 2 is remarkably shorter than thegraph length of the other sheet material. From this, when the mixedamount of the matrix is increased too much, it is found that thefracture ductility is reduced more.

Then, when looking at the stress of Sheet material 1 to 5 that thestrain corresponds to “0.02” for example, the graph position of theother sheet material is more above than the graph position of Sheetmaterial 5. From this, when the matrix is mixed, it is found that thestress against the strain is improved.

TABLE 4 Sheet material Tensile strength [MPa] Tensile elasticity [MPa]Sheet material 1 42.0 1483 Sheet material 2 26.0 2065 Sheet material 336.5 2044 Sheet material 4 47.5 1942 Sheet material 5 26.6 1541

Table 4 is a table showing the calculation results of the tensilestrength [MPa] and the tensile elasticity [MPa] of Sheet material 1 toSheet material 5. As shown in Table 4, since the tensile strength ofSheet material 1, 3 and 4 is improved, in general, the tensile strengthis improved by mixing the matrix. However, from the fact that thetensile strength of Sheet material 2 is reduced, when the mixed amountof the matrix is increased too much, it is considered that the tensilestrength is reduced.

From the above, in the fields that the high tensile strength, or, thestress against the strain are required, although it depends onapplications of the sheet material, it is better to mix the appropriateamount of matrix. On the other hand, in the field that the high fractureductility is required, although it depends on applications of the sheetmaterial, it is better not to mix the matrix.

INDUSTRIAL APPLICABILITY

The present invention has applicability in the field of electromagneticshielding and in the field of electromagnetic wave absorption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic production process diagram of the sheetmaterial using the burned material of cacao husk.

FIG. 2 shows charts indicating the measurement results of theelectromagnetic shielding characteristics of the sheet material producedthrough a pulverization process of burned material of cacao husk.

FIG. 3 shows charts indicating the measurement results of theelectromagnetic shielding characteristics of the sheet material producedwithout going through a pulverization process of burned material ofcacao husk.

FIG. 4 shows charts indicating the measurement results of theelectromagnetic shielding characteristics of the sheet material producedthrough a pulverization process of burned material of soybean hulls.

FIG. 5 shows charts indicating the measurement results of theelectromagnetic shielding characteristics of the sheet material producedwithout going through a pulverization process of burned material ofsoybean hulls.

FIG. 6 shows charts indicating the measurement results of theelectromagnetic wave absorption characteristic of the sheet materialproduced through a pulverization process of burned material of cacaohusk.

FIG. 7 shows charts indicating the measurement results of theelectromagnetic wave absorption characteristic of the sheet materialproduced through a pulverization process of the burned material of ricehusk.

FIG. 8 shows charts indicating the measurement results of theelectromagnetic wave absorption characteristic of the sheet materialproduced by using the burned material of rice bran.

FIG. 9 shows charts indicating the results of component analysis basedon the ZAF quantitative analysis method for cacao husk before and afterburning.

FIG. 10 shows charts indicating the result of the component analysisbased on the organic micro-elemental analysis method corresponding toFIG. 9.

FIG. 11 shows a chart indicating the test results of the conductivitytest regarding the burned material of cacao husk after pulverization.

FIG. 12 shows a chart indicating the relationship between the contentratio of the burned material of cacao husk kneaded into ethylenepropylene diene terpolymer and the specific volume resistivity.

FIG. 13 shows SEM pictures of cacao husk before burning.

FIG. 14 shows SEM pictures of cacao husk before burning.

FIG. 15 shows SEM pictures of cacao husk burned without distinguishingby the inner skin and the outer skin.

FIG. 16 shows SEM pictures of cacao husk burned without distinguishingby the inner skin and the outer skin.

FIG. 17 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material accordingto 1^(st) category shown in Table 1.

FIG. 18 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material accordingto 2^(nd) category shown in Table 1, it is corresponding to FIG. 17.

FIG. 19 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material accordingto 3^(rd) category shown in Table 1.

FIG. 20 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material accordingto 4^(th) category shown in Table 2.

FIG. 21 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material withoutaddition of stainless fiber against burned material of cacao huskwithout performing the pulverization treatment.

FIG. 22 is figures showing the measurement results of theelectromagnetic shielding effectiveness of the sheet material withaddition of stainless fiber against burned material of cacao huskwithout performing the pulverization treatment.

FIG. 23 is a figure showing the electromagnetic shielding characteristicof the sheet material consisting of the mixture of the burned plantmaterial and SUS fiber measured based on the arch test method.

FIG. 24 is a figure showing the electromagnetic shielding characteristicfor the laminate consisting of the sheet material produced from a singlesubstance of SUS fiber and the sheet material produced from a singlesubstance of burned plant material measured based on the arch testmethod as a comparative example.

FIG. 25 is a figure showing the measurement results of the specificvolume resistivity of the sheet material consisting of cacao husk whichwas burned after performing the pulverization process. It is a figureshowing the measurement results of the specific volume resistivity ofthe sheet material.

FIG. 26 is a figure showing the specific volume resistivity of Sheetmaterial 1 to Sheet material 5.

FIG. 27 is a figure showing the electromagnetic shielding effectivenessof Sheet material 1 to Sheet material 5.

FIG. 28 is a schematic diagram of workpiece for tensile test of Sheetmaterial 1 to Sheet material 5.

FIG. 29 is a figure showing the test results of tensile test of Sheetmaterial 1 to Sheet material 5.

1. A sheet material formed by a wet-process sheet production method from a mixture of burned plant material and fibrous material.
 2. The sheet material as claimed in claim 1, wherein the burned plant material is a burned material of rice husk, a burned material of rice bran, a burned material of soybean hulls, a burned material of rapeseed meal, a burned material of inner skin of peanut, a burned material of conduit side wall portion of seed plant, or a burned material of cacao husk.
 3. The sheet material as claimed in claim 1, wherein the burned plant material contains a spiral portion.
 4. The sheet material as claimed in claim 1, wherein the fibrous material is a thermoplastic resin fiber, a thermosetting resin fiber, a natural fiber, a semisynthetic fiber, a glass fiber, an inorganic fiber, a metal fiber, or one of these combinations.
 5. The sheet material as claimed in claim 1, in addition, wherein a metal filler is mixed.
 6. The sheet material as claimed in claim 1, wherein a mixing ratio of the fibrous material and the metal filler is 1:3 to 3:1.
 7. The sheet material as claimed in claim 1, wherein, after the wet-process sheet production, the sheet material is pressurized under a condition that a bulk density becomes 0.5 [g/cm³] or above.
 8. The sheet material as claimed in claim 1, wherein, in addition, a matrix consisting of a thermosetting resin, or, a thermoplastic resin is mixed.
 9. A burned plant material included in the sheet material as claimed in claim
 1. 10. A method producing for a sheet material, wherein the method is to form a sheet by wet-process sheet production using a sheet making slurry obtained by mixing a fibrous material and a burned plant material in water.
 11. An electromagnetic shielding member, wherein the electromagnetic shielding member consists of a sheet material using a burned plant material.
 12. An electromagnetic shielding member consisting of a sheet material formed by a wet-process sheet production method from a mixture of burned plant material, fibrous material and metal filler.
 13. An electromagnetic shielding member laminated a sheet material using a burned plant material and a sheet material formed by a wet-process sheet production method from a mixture of burned plant material, fibrous material and metal filler. 